// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Package core implements the Ethereum consensus protocol.
package core

import (
	"errors"
	"fmt"
	"io"
	"math/big"
	mrand "math/rand"
	"sync"
	"sync/atomic"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/mclock"
	"github.com/ethereum/go-ethereum/consensus"
	"github.com/ethereum/go-ethereum/core/state"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/core/vm"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/event"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/metrics"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/ethereum/go-ethereum/trie"
	"github.com/hashicorp/golang-lru"
)

var (
	blockInsertTimer = metrics.NewTimer("chain/inserts")

	ErrNoGenesis = errors.New("Genesis not found in chain")
)

const (
	bodyCacheLimit      = 256
	blockCacheLimit     = 256
	maxFutureBlocks     = 256
	maxTimeFutureBlocks = 30
	badBlockLimit       = 10

	// BlockChainVersion ensures that an incompatible database forces a resync from scratch.
	BlockChainVersion = 3
)

// BlockChain represents the canonical chain given a database with a genesis
// block. The Blockchain manages chain imports, reverts, chain reorganisations.
// BlockChain 表示了一个规范的链，这个链通过一个包含了创世区块的数据库指定。
// BlockChain 管理了链的插入，还原，重建等操作。
// Importing blocks in to the block chain happens according to the set of rules
// defined by the two stage Validator. Processing of blocks is done using the
// Processor which processes the included transaction. The validation of the state
// is done in the second part of the Validator. Failing results in aborting of
// the import.
// 插入一个区块需要通过一系列指定的规则指定的两阶段的验证器。
// 使用 Processor 来对区块的交易进行处理。状态的验证是第二阶段的验证器。错误将导致插入终止。
// The BlockChain also helps in returning blocks from **any** chain included
// in the database as well as blocks that represents the canonical chain. It's
// important to note that GetBlock can return any block and does not need to be
// included in the canonical one where as GetBlockByNumber always represents the
// canonical chain.
// 需要注意的是 GetBlock 可能返回任意不在当前规范区块链中的区块，
// 但是 GetBlockByNumber 总是返回当前规范区块链中的区块。
type BlockChain struct {
	config *params.ChainConfig // chain & network configuration
	// 只包含了区块头的区块链
	hc            *HeaderChain
	// 底层数据库
	chainDb       ethdb.Database
	// 下面是很多消息通知的组件
	rmLogsFeed    event.Feed
	chainFeed     event.Feed
	chainSideFeed event.Feed
	chainHeadFeed event.Feed
	logsFeed      event.Feed
	scope         event.SubscriptionScope
	// 创世区块
	genesisBlock  *types.Block

	mu      sync.RWMutex // global mutex for locking chain operations
	chainmu sync.RWMutex // blockchain insertion lock
	procmu  sync.RWMutex // block processor lock

	checkpoint       int          // checkpoint counts towards the new checkpoint
	// 当前的区块头
	currentBlock     *types.Block // Current head of the block chain
	// 当前的快速同步的区块头
	currentFastBlock *types.Block // Current head of the fast-sync chain (may be above the block chain!)

	stateCache   state.Database // State database to reuse between imports (contains state cache)
	bodyCache    *lru.Cache     // Cache for the most recent block bodies
	bodyRLPCache *lru.Cache     // Cache for the most recent block bodies in RLP encoded format
	blockCache   *lru.Cache     // Cache for the most recent entire blocks
	// 暂时还不能插入的区块存放位置
	futureBlocks *lru.Cache     // future blocks are blocks added for later processing

	quit    chan struct{} // blockchain quit channel
	running int32         // running must be called atomically
	// procInterrupt must be atomically called
	procInterrupt int32          // interrupt signaler for block processing
	wg            sync.WaitGroup // chain processing wait group for shutting down
	// 共识引擎
	engine    consensus.Engine
	// 区块处理器接口
	processor Processor // block processor interface
	// 区块和状态验证器接口
	validator Validator // block and state validator interface
	// 虚拟机的配置
	vmConfig  vm.Config
	// 错误区块的缓存
	badBlocks *lru.Cache // Bad block cache
}

// NewBlockChain returns a fully initialised block chain using information
// available in the database. It initialises the default Ethereum Validator and
// Processor.
// 新建区块链
func NewBlockChain(chainDb ethdb.Database, config *params.ChainConfig, engine consensus.Engine, vmConfig vm.Config) (*BlockChain, error) {
	bodyCache, _ := lru.New(bodyCacheLimit)
	bodyRLPCache, _ := lru.New(bodyCacheLimit)
	blockCache, _ := lru.New(blockCacheLimit)
	futureBlocks, _ := lru.New(maxFutureBlocks)
	badBlocks, _ := lru.New(badBlockLimit)

	bc := &BlockChain{
		config:       config,
		chainDb:      chainDb,
		stateCache:   state.NewDatabase(chainDb),
		quit:         make(chan struct{}),
		bodyCache:    bodyCache,
		bodyRLPCache: bodyRLPCache,
		blockCache:   blockCache,
		futureBlocks: futureBlocks,
		engine:       engine,
		vmConfig:     vmConfig,
		badBlocks:    badBlocks,
	}
	bc.SetValidator(NewBlockValidator(config, bc, engine))
	bc.SetProcessor(NewStateProcessor(config, bc, engine))

	var err error
	bc.hc, err = NewHeaderChain(chainDb, config, engine, bc.getProcInterrupt)
	if err != nil {
		return nil, err
	}
	// 获取创世区块
	bc.genesisBlock = bc.GetBlockByNumber(0)
	if bc.genesisBlock == nil {
		return nil, ErrNoGenesis
	}
	// 获取最新状态
	if err := bc.loadLastState(); err != nil {
		return nil, err
	}
	// Check the current state of the block hashes and make sure that we do not have any of the bad blocks in our chain
	// 检测是否有坏区块
	// 检查当前的状态，确认我们的区块链上面没有非法的区块。
	// BadHashes 是一些手工配置的区块 hash 值，用来硬分叉使用的。
	for hash := range BadHashes {
		if header := bc.GetHeaderByHash(hash); header != nil {
			// get the canonical block corresponding to the offending header's number
			// 获取规范的区块链上面同样高度的区块头，如果这个区块头
			// 确实是在我们的规范的区块链上的话，我们需要回滚到这个区块头的高度 - 1
			headerByNumber := bc.GetHeaderByNumber(header.Number.Uint64())
			// make sure the headerByNumber (if present) is in our current canonical chain
			if headerByNumber != nil && headerByNumber.Hash() == header.Hash() {
				log.Error("Found bad hash, rewinding chain", "number", header.Number, "hash", header.ParentHash)
				bc.SetHead(header.Number.Uint64() - 1)
				log.Error("Chain rewind was successful, resuming normal operation")
			}
		}
	}
	// Take ownership of this particular state
	go bc.update()
	return bc, nil
}

func (bc *BlockChain) getProcInterrupt() bool {
	return atomic.LoadInt32(&bc.procInterrupt) == 1
}

// loadLastState loads the last known chain state from the database. This method
// assumes that the chain manager mutex is held.
func (bc *BlockChain) loadLastState() error {
	// Restore the last known head block
	// 返回我们知道的最新的区块的 hash
	head := GetHeadBlockHash(bc.chainDb)
	// 如果获取到了空，那么认为数据库已经被破坏。那么设置区块链为创世区块。
	if head == (common.Hash{}) {
		// Corrupt or empty database, init from scratch
		log.Warn("Empty database, resetting chain")
		return bc.Reset()
	}
	// Make sure the entire head block is available
	// 根据 blockHash 来查找 block
	currentBlock := bc.GetBlockByHash(head)
	if currentBlock == nil {
		// Corrupt or empty database, init from scratch
		log.Warn("Head block missing, resetting chain", "hash", head)
		return bc.Reset()
	}
	// Make sure the state associated with the block is available
	// 确认和这个区块的 world state 是否正确
	if _, err := state.New(currentBlock.Root(), bc.stateCache); err != nil {
		// Dangling block without a state associated, init from scratch
		log.Warn("Head state missing, resetting chain", "number", currentBlock.Number(), "hash", currentBlock.Hash())
		return bc.Reset()
	}
	// Everything seems to be fine, set as the head block
	bc.currentBlock = currentBlock

	// Restore the last known head header
	// 获取最新的区块头的 hash
	currentHeader := bc.currentBlock.Header()
	if head := GetHeadHeaderHash(bc.chainDb); head != (common.Hash{}) {
		if header := bc.GetHeaderByHash(head); header != nil {
			currentHeader = header
		}
	}
	// header chain 设置为当前的区块头
	bc.hc.SetCurrentHeader(currentHeader)

	// Restore the last known head fast block
	bc.currentFastBlock = bc.currentBlock
	if head := GetHeadFastBlockHash(bc.chainDb); head != (common.Hash{}) {
		if block := bc.GetBlockByHash(head); block != nil {
			bc.currentFastBlock = block
		}
	}

	// Issue a status log for the user
	// 用来打印日志
	headerTd := bc.GetTd(currentHeader.Hash(), currentHeader.Number.Uint64())
	blockTd := bc.GetTd(bc.currentBlock.Hash(), bc.currentBlock.NumberU64())
	fastTd := bc.GetTd(bc.currentFastBlock.Hash(), bc.currentFastBlock.NumberU64())

	log.Info("Loaded most recent local header", "number", currentHeader.Number, "hash", currentHeader.Hash(), "td", headerTd)
	log.Info("Loaded most recent local full block", "number", bc.currentBlock.Number(), "hash", bc.currentBlock.Hash(), "td", blockTd)
	log.Info("Loaded most recent local fast block", "number", bc.currentFastBlock.Number(), "hash", bc.currentFastBlock.Hash(), "td", fastTd)

	return nil
}

// SetHead rewinds the local chain to a new head. In the case of headers, everything
// above the new head will be deleted and the new one set. In the case of blocks
// though, the head may be further rewound if block bodies are missing (non-archive
// nodes after a fast sync).
func (bc *BlockChain) SetHead(head uint64) error {
	log.Warn("Rewinding blockchain", "target", head)

	bc.mu.Lock()
	defer bc.mu.Unlock()

	// Rewind the header chain, deleting all block bodies until then
	delFn := func(hash common.Hash, num uint64) {
		DeleteBody(bc.chainDb, hash, num)
	}
	bc.hc.SetHead(head, delFn)
	currentHeader := bc.hc.CurrentHeader()

	// Clear out any stale content from the caches
	bc.bodyCache.Purge()
	bc.bodyRLPCache.Purge()
	bc.blockCache.Purge()
	bc.futureBlocks.Purge()

	// Rewind the block chain, ensuring we don't end up with a stateless head block
	if bc.currentBlock != nil && currentHeader.Number.Uint64() < bc.currentBlock.NumberU64() {
		bc.currentBlock = bc.GetBlock(currentHeader.Hash(), currentHeader.Number.Uint64())
	}
	if bc.currentBlock != nil {
		if _, err := state.New(bc.currentBlock.Root(), bc.stateCache); err != nil {
			// Rewound state missing, rolled back to before pivot, reset to genesis
			bc.currentBlock = nil
		}
	}
	// Rewind the fast block in a simpleton way to the target head
	if bc.currentFastBlock != nil && currentHeader.Number.Uint64() < bc.currentFastBlock.NumberU64() {
		bc.currentFastBlock = bc.GetBlock(currentHeader.Hash(), currentHeader.Number.Uint64())
	}
	// If either blocks reached nil, reset to the genesis state
	if bc.currentBlock == nil {
		bc.currentBlock = bc.genesisBlock
	}
	if bc.currentFastBlock == nil {
		bc.currentFastBlock = bc.genesisBlock
	}
	if err := WriteHeadBlockHash(bc.chainDb, bc.currentBlock.Hash()); err != nil {
		log.Crit("Failed to reset head full block", "err", err)
	}
	if err := WriteHeadFastBlockHash(bc.chainDb, bc.currentFastBlock.Hash()); err != nil {
		log.Crit("Failed to reset head fast block", "err", err)
	}
	return bc.loadLastState()
}

// FastSyncCommitHead sets the current head block to the one defined by the hash
// irrelevant what the chain contents were prior.
func (bc *BlockChain) FastSyncCommitHead(hash common.Hash) error {
	// Make sure that both the block as well at its state trie exists
	block := bc.GetBlockByHash(hash)
	if block == nil {
		return fmt.Errorf("non existent block [%x…]", hash[:4])
	}
	if _, err := trie.NewSecure(block.Root(), bc.chainDb, 0); err != nil {
		return err
	}
	// If all checks out, manually set the head block
	bc.mu.Lock()
	bc.currentBlock = block
	bc.mu.Unlock()

	log.Info("Committed new head block", "number", block.Number(), "hash", hash)
	return nil
}

// GasLimit returns the gas limit of the current HEAD block.
func (bc *BlockChain) GasLimit() *big.Int {
	bc.mu.RLock()
	defer bc.mu.RUnlock()

	return bc.currentBlock.GasLimit()
}

// LastBlockHash return the hash of the HEAD block.
func (bc *BlockChain) LastBlockHash() common.Hash {
	bc.mu.RLock()
	defer bc.mu.RUnlock()

	return bc.currentBlock.Hash()
}

// CurrentBlock retrieves the current head block of the canonical chain. The
// block is retrieved from the blockchain's internal cache.
func (bc *BlockChain) CurrentBlock() *types.Block {
	bc.mu.RLock()
	defer bc.mu.RUnlock()

	return bc.currentBlock
}

// CurrentFastBlock retrieves the current fast-sync head block of the canonical
// chain. The block is retrieved from the blockchain's internal cache.
func (bc *BlockChain) CurrentFastBlock() *types.Block {
	bc.mu.RLock()
	defer bc.mu.RUnlock()

	return bc.currentFastBlock
}

// Status returns status information about the current chain such as the HEAD Td,
// the HEAD hash and the hash of the genesis block.
func (bc *BlockChain) Status() (td *big.Int, currentBlock common.Hash, genesisBlock common.Hash) {
	bc.mu.RLock()
	defer bc.mu.RUnlock()

	return bc.GetTd(bc.currentBlock.Hash(), bc.currentBlock.NumberU64()), bc.currentBlock.Hash(), bc.genesisBlock.Hash()
}

// SetProcessor sets the processor required for making state modifications.
func (bc *BlockChain) SetProcessor(processor Processor) {
	bc.procmu.Lock()
	defer bc.procmu.Unlock()
	bc.processor = processor
}

// SetValidator sets the validator which is used to validate incoming blocks.
func (bc *BlockChain) SetValidator(validator Validator) {
	bc.procmu.Lock()
	defer bc.procmu.Unlock()
	bc.validator = validator
}

// Validator returns the current validator.
func (bc *BlockChain) Validator() Validator {
	bc.procmu.RLock()
	defer bc.procmu.RUnlock()
	return bc.validator
}

// Processor returns the current processor.
func (bc *BlockChain) Processor() Processor {
	bc.procmu.RLock()
	defer bc.procmu.RUnlock()
	return bc.processor
}

// State returns a new mutable state based on the current HEAD block.
func (bc *BlockChain) State() (*state.StateDB, error) {
	return bc.StateAt(bc.CurrentBlock().Root())
}

// StateAt returns a new mutable state based on a particular point in time.
func (bc *BlockChain) StateAt(root common.Hash) (*state.StateDB, error) {
	return state.New(root, bc.stateCache)
}

// Reset purges the entire blockchain, restoring it to its genesis state.
// 重置清除整个区块链，将其恢复到其创世状态。
func (bc *BlockChain) Reset() error {
	return bc.ResetWithGenesisBlock(bc.genesisBlock)
}

// ResetWithGenesisBlock purges the entire blockchain, restoring it to the
// specified genesis state.
// ResetWithGenesisBlock 清除整个区块链，将其恢复到指定的创世状态。
func (bc *BlockChain) ResetWithGenesisBlock(genesis *types.Block) error {
	// Dump the entire block chain and purge the caches
	// 把整个区块链转储并清楚缓存
	if err := bc.SetHead(0); err != nil {
		return err
	}
	bc.mu.Lock()
	defer bc.mu.Unlock()

	// Prepare the genesis block and reinitialise the chain
	// 使用创世区块重新初始化区块链
	if err := bc.hc.WriteTd(genesis.Hash(), genesis.NumberU64(), genesis.Difficulty()); err != nil {
		log.Crit("Failed to write genesis block TD", "err", err)
	}
	if err := WriteBlock(bc.chainDb, genesis); err != nil {
		log.Crit("Failed to write genesis block", "err", err)
	}
	bc.genesisBlock = genesis
	bc.insert(bc.genesisBlock)
	bc.currentBlock = bc.genesisBlock
	bc.hc.SetGenesis(bc.genesisBlock.Header())
	bc.hc.SetCurrentHeader(bc.genesisBlock.Header())
	bc.currentFastBlock = bc.genesisBlock

	return nil
}

// Export writes the active chain to the given writer.
func (bc *BlockChain) Export(w io.Writer) error {
	return bc.ExportN(w, uint64(0), bc.currentBlock.NumberU64())
}

// ExportN writes a subset of the active chain to the given writer.
func (bc *BlockChain) ExportN(w io.Writer, first uint64, last uint64) error {
	bc.mu.RLock()
	defer bc.mu.RUnlock()

	if first > last {
		return fmt.Errorf("export failed: first (%d) is greater than last (%d)", first, last)
	}
	log.Info("Exporting batch of blocks", "count", last-first+1)

	for nr := first; nr <= last; nr++ {
		block := bc.GetBlockByNumber(nr)
		if block == nil {
			return fmt.Errorf("export failed on #%d: not found", nr)
		}

		if err := block.EncodeRLP(w); err != nil {
			return err
		}
	}

	return nil
}

// insert injects a new head block into the current block chain. This method
// assumes that the block is indeed a true head. It will also reset the head
// header and the head fast sync block to this very same block if they are older
// or if they are on a different side chain.
//
// Note, this function assumes that the `mu` mutex is held!
func (bc *BlockChain) insert(block *types.Block) {
	// If the block is on a side chain or an unknown one, force other heads onto it too
	updateHeads := GetCanonicalHash(bc.chainDb, block.NumberU64()) != block.Hash()

	// Add the block to the canonical chain number scheme and mark as the head
	if err := WriteCanonicalHash(bc.chainDb, block.Hash(), block.NumberU64()); err != nil {
		log.Crit("Failed to insert block number", "err", err)
	}
	if err := WriteHeadBlockHash(bc.chainDb, block.Hash()); err != nil {
		log.Crit("Failed to insert head block hash", "err", err)
	}
	bc.currentBlock = block

	// If the block is better than out head or is on a different chain, force update heads
	if updateHeads {
		bc.hc.SetCurrentHeader(block.Header())

		if err := WriteHeadFastBlockHash(bc.chainDb, block.Hash()); err != nil {
			log.Crit("Failed to insert head fast block hash", "err", err)
		}
		bc.currentFastBlock = block
	}
}

// Genesis retrieves the chain's genesis block.
func (bc *BlockChain) Genesis() *types.Block {
	return bc.genesisBlock
}

// GetBody retrieves a block body (transactions and uncles) from the database by
// hash, caching it if found.
func (bc *BlockChain) GetBody(hash common.Hash) *types.Body {
	// Short circuit if the body's already in the cache, retrieve otherwise
	if cached, ok := bc.bodyCache.Get(hash); ok {
		body := cached.(*types.Body)
		return body
	}
	body := GetBody(bc.chainDb, hash, bc.hc.GetBlockNumber(hash))
	if body == nil {
		return nil
	}
	// Cache the found body for next time and return
	bc.bodyCache.Add(hash, body)
	return body
}

// GetBodyRLP retrieves a block body in RLP encoding from the database by hash,
// caching it if found.
func (bc *BlockChain) GetBodyRLP(hash common.Hash) rlp.RawValue {
	// Short circuit if the body's already in the cache, retrieve otherwise
	if cached, ok := bc.bodyRLPCache.Get(hash); ok {
		return cached.(rlp.RawValue)
	}
	body := GetBodyRLP(bc.chainDb, hash, bc.hc.GetBlockNumber(hash))
	if len(body) == 0 {
		return nil
	}
	// Cache the found body for next time and return
	bc.bodyRLPCache.Add(hash, body)
	return body
}

// HasBlock checks if a block is fully present in the database or not.
func (bc *BlockChain) HasBlock(hash common.Hash, number uint64) bool {
	if bc.blockCache.Contains(hash) {
		return true
	}
	ok, _ := bc.chainDb.Has(blockBodyKey(hash, number))
	return ok
}

// HasBlockAndState checks if a block and associated state trie is fully present
// in the database or not, caching it if present.
func (bc *BlockChain) HasBlockAndState(hash common.Hash) bool {
	// Check first that the block itself is known
	block := bc.GetBlockByHash(hash)
	if block == nil {
		return false
	}
	// Ensure the associated state is also present
	_, err := bc.stateCache.OpenTrie(block.Root())
	return err == nil
}

// GetBlock retrieves a block from the database by hash and number,
// caching it if found.
func (bc *BlockChain) GetBlock(hash common.Hash, number uint64) *types.Block {
	// Short circuit if the block's already in the cache, retrieve otherwise
	if block, ok := bc.blockCache.Get(hash); ok {
		return block.(*types.Block)
	}
	block := GetBlock(bc.chainDb, hash, number)
	if block == nil {
		return nil
	}
	// Cache the found block for next time and return
	bc.blockCache.Add(block.Hash(), block)
	return block
}

// GetBlockByHash retrieves a block from the database by hash, caching it if found.
func (bc *BlockChain) GetBlockByHash(hash common.Hash) *types.Block {
	return bc.GetBlock(hash, bc.hc.GetBlockNumber(hash))
}

// GetBlockByNumber retrieves a block from the database by number, caching it
// (associated with its hash) if found.
func (bc *BlockChain) GetBlockByNumber(number uint64) *types.Block {
	hash := GetCanonicalHash(bc.chainDb, number)
	if hash == (common.Hash{}) {
		return nil
	}
	return bc.GetBlock(hash, number)
}

// GetBlocksFromHash returns the block corresponding to hash and up to n-1 ancestors.
// [deprecated by eth/62]
func (bc *BlockChain) GetBlocksFromHash(hash common.Hash, n int) (blocks []*types.Block) {
	number := bc.hc.GetBlockNumber(hash)
	for i := 0; i < n; i++ {
		block := bc.GetBlock(hash, number)
		if block == nil {
			break
		}
		blocks = append(blocks, block)
		hash = block.ParentHash()
		number--
	}
	return
}

// GetUnclesInChain retrieves all the uncles from a given block backwards until
// a specific distance is reached.
func (bc *BlockChain) GetUnclesInChain(block *types.Block, length int) []*types.Header {
	uncles := []*types.Header{}
	for i := 0; block != nil && i < length; i++ {
		uncles = append(uncles, block.Uncles()...)
		block = bc.GetBlock(block.ParentHash(), block.NumberU64()-1)
	}
	return uncles
}

// Stop stops the blockchain service. If any imports are currently in progress
// it will abort them using the procInterrupt.
func (bc *BlockChain) Stop() {
	if !atomic.CompareAndSwapInt32(&bc.running, 0, 1) {
		return
	}
	// Unsubscribe all subscriptions registered from blockchain
	bc.scope.Close()
	close(bc.quit)
	atomic.StoreInt32(&bc.procInterrupt, 1)

	bc.wg.Wait()
	log.Info("Blockchain manager stopped")
}

func (bc *BlockChain) procFutureBlocks() {
	blocks := make([]*types.Block, 0, bc.futureBlocks.Len())
	for _, hash := range bc.futureBlocks.Keys() {
		if block, exist := bc.futureBlocks.Peek(hash); exist {
			blocks = append(blocks, block.(*types.Block))
		}
	}
	if len(blocks) > 0 {
		types.BlockBy(types.Number).Sort(blocks)

		// Insert one by one as chain insertion needs contiguous ancestry between blocks
		for i := range blocks {
			bc.InsertChain(blocks[i : i+1])
		}
	}
}

// WriteStatus status of write
type WriteStatus byte

const (
	NonStatTy WriteStatus = iota
	CanonStatTy
	SideStatTy
)

// Rollback is designed to remove a chain of links from the database that aren't
// certain enough to be valid.
func (bc *BlockChain) Rollback(chain []common.Hash) {
	bc.mu.Lock()
	defer bc.mu.Unlock()

	for i := len(chain) - 1; i >= 0; i-- {
		hash := chain[i]

		currentHeader := bc.hc.CurrentHeader()
		if currentHeader.Hash() == hash {
			bc.hc.SetCurrentHeader(bc.GetHeader(currentHeader.ParentHash, currentHeader.Number.Uint64()-1))
		}
		if bc.currentFastBlock.Hash() == hash {
			bc.currentFastBlock = bc.GetBlock(bc.currentFastBlock.ParentHash(), bc.currentFastBlock.NumberU64()-1)
			WriteHeadFastBlockHash(bc.chainDb, bc.currentFastBlock.Hash())
		}
		if bc.currentBlock.Hash() == hash {
			bc.currentBlock = bc.GetBlock(bc.currentBlock.ParentHash(), bc.currentBlock.NumberU64()-1)
			WriteHeadBlockHash(bc.chainDb, bc.currentBlock.Hash())
		}
	}
}

// SetReceiptsData computes all the non-consensus fields of the receipts
func SetReceiptsData(config *params.ChainConfig, block *types.Block, receipts types.Receipts) {
	signer := types.MakeSigner(config, block.Number())

	transactions, logIndex := block.Transactions(), uint(0)

	for j := 0; j < len(receipts); j++ {
		// The transaction hash can be retrieved from the transaction itself
		receipts[j].TxHash = transactions[j].Hash()

		// The contract address can be derived from the transaction itself
		if transactions[j].To() == nil {
			// Deriving the signer is expensive, only do if it's actually needed
			from, _ := types.Sender(signer, transactions[j])
			receipts[j].ContractAddress = crypto.CreateAddress(from, transactions[j].Nonce())
		}
		// The used gas can be calculated based on previous receipts
		if j == 0 {
			receipts[j].GasUsed = new(big.Int).Set(receipts[j].CumulativeGasUsed)
		} else {
			receipts[j].GasUsed = new(big.Int).Sub(receipts[j].CumulativeGasUsed, receipts[j-1].CumulativeGasUsed)
		}
		// The derived log fields can simply be set from the block and transaction
		for k := 0; k < len(receipts[j].Logs); k++ {
			receipts[j].Logs[k].BlockNumber = block.NumberU64()
			receipts[j].Logs[k].BlockHash = block.Hash()
			receipts[j].Logs[k].TxHash = receipts[j].TxHash
			receipts[j].Logs[k].TxIndex = uint(j)
			receipts[j].Logs[k].Index = logIndex
			logIndex++
		}
	}
}

// InsertReceiptChain attempts to complete an already existing header chain with
// transaction and receipt data.
func (bc *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain []types.Receipts) (int, error) {
	bc.wg.Add(1)
	defer bc.wg.Done()

	// Do a sanity check that the provided chain is actually ordered and linked
	for i := 1; i < len(blockChain); i++ {
		if blockChain[i].NumberU64() != blockChain[i-1].NumberU64()+1 || blockChain[i].ParentHash() != blockChain[i-1].Hash() {
			log.Error("Non contiguous receipt insert", "number", blockChain[i].Number(), "hash", blockChain[i].Hash(), "parent", blockChain[i].ParentHash(),
				"prevnumber", blockChain[i-1].Number(), "prevhash", blockChain[i-1].Hash())
			return 0, fmt.Errorf("non contiguous insert: item %d is #%d [%x…], item %d is #%d [%x…] (parent [%x…])", i-1, blockChain[i-1].NumberU64(),
				blockChain[i-1].Hash().Bytes()[:4], i, blockChain[i].NumberU64(), blockChain[i].Hash().Bytes()[:4], blockChain[i].ParentHash().Bytes()[:4])
		}
	}

	var (
		stats = struct{ processed, ignored int32 }{}
		start = time.Now()
		bytes = 0
		batch = bc.chainDb.NewBatch()
	)
	for i, block := range blockChain {
		receipts := receiptChain[i]
		// Short circuit insertion if shutting down or processing failed
		if atomic.LoadInt32(&bc.procInterrupt) == 1 {
			return 0, nil
		}
		// Short circuit if the owner header is unknown
		if !bc.HasHeader(block.Hash(), block.NumberU64()) {
			return i, fmt.Errorf("containing header #%d [%x…] unknown", block.Number(), block.Hash().Bytes()[:4])
		}
		// Skip if the entire data is already known
		if bc.HasBlock(block.Hash(), block.NumberU64()) {
			stats.ignored++
			continue
		}
		// Compute all the non-consensus fields of the receipts
		SetReceiptsData(bc.config, block, receipts)
		// Write all the data out into the database
		if err := WriteBody(batch, block.Hash(), block.NumberU64(), block.Body()); err != nil {
			return i, fmt.Errorf("failed to write block body: %v", err)
		}
		if err := WriteBlockReceipts(batch, block.Hash(), block.NumberU64(), receipts); err != nil {
			return i, fmt.Errorf("failed to write block receipts: %v", err)
		}
		if err := WriteTxLookupEntries(batch, block); err != nil {
			return i, fmt.Errorf("failed to write lookup metadata: %v", err)
		}
		stats.processed++

		if batch.ValueSize() >= ethdb.IdealBatchSize {
			if err := batch.Write(); err != nil {
				return 0, err
			}
			bytes += batch.ValueSize()
			batch = bc.chainDb.NewBatch()
		}
	}
	if batch.ValueSize() > 0 {
		bytes += batch.ValueSize()
		if err := batch.Write(); err != nil {
			return 0, err
		}
	}

	// Update the head fast sync block if better
	bc.mu.Lock()
	head := blockChain[len(blockChain)-1]
	if td := bc.GetTd(head.Hash(), head.NumberU64()); td != nil { // Rewind may have occurred, skip in that case
		if bc.GetTd(bc.currentFastBlock.Hash(), bc.currentFastBlock.NumberU64()).Cmp(td) < 0 {
			if err := WriteHeadFastBlockHash(bc.chainDb, head.Hash()); err != nil {
				log.Crit("Failed to update head fast block hash", "err", err)
			}
			bc.currentFastBlock = head
		}
	}
	bc.mu.Unlock()

	log.Info("Imported new block receipts",
		"count", stats.processed,
		"elapsed", common.PrettyDuration(time.Since(start)),
		"bytes", bytes,
		"number", head.Number(),
		"hash", head.Hash(),
		"ignored", stats.ignored)
	return 0, nil
}

// WriteBlock writes the block to the chain.
// 把区块写入区块链
func (bc *BlockChain) WriteBlockAndState(block *types.Block, receipts []*types.Receipt, state *state.StateDB) (status WriteStatus, err error) {
	bc.wg.Add(1)
	defer bc.wg.Done()

	// Calculate the total difficulty of the block
	// 计算待插入的区块的总难度
	ptd := bc.GetTd(block.ParentHash(), block.NumberU64()-1)
	if ptd == nil {
		return NonStatTy, consensus.ErrUnknownAncestor
	}
	// Make sure no inconsistent state is leaked during insertion
	// 确保在插入过程中没有不一致的状态泄漏
	bc.mu.Lock()
	defer bc.mu.Unlock()
	// 计算当前区块的区块链的总难度
	localTd := bc.GetTd(bc.currentBlock.Hash(), bc.currentBlock.NumberU64())
	// 计算新的区块链的总难度
	externTd := new(big.Int).Add(block.Difficulty(), ptd)

	// Irrelevant of the canonical status, write the block itself to the database
	// 和规范区块没有关系的状态, 写入数据库.  写入区块的 hash 高度和对应的总难度
	if err := bc.hc.WriteTd(block.Hash(), block.NumberU64(), externTd); err != nil {
		return NonStatTy, err
	}
	// Write other block data using a batch.
	batch := bc.chainDb.NewBatch()
	// 写入区块
	if err := WriteBlock(batch, block); err != nil {
		return NonStatTy, err
	}
	if _, err := state.CommitTo(batch, bc.config.IsEIP158(block.Number())); err != nil {
		return NonStatTy, err
	}
	// 写入区块收据
	if err := WriteBlockReceipts(batch, block.Hash(), block.NumberU64(), receipts); err != nil {
		return NonStatTy, err
	}

	// If the total difficulty is higher than our known, add it to the canonical chain
	// Second clause in the if statement reduces the vulnerability to selfish mining.
	// Please refer to http://www.cs.cornell.edu/~ie53/publications/btcProcFC.pdf
	// 如果新的区块的总难度高于我们当前的区块，把这个区块设置为规范的区块。
	// 第二个表达式 ((externTd.Cmp(localTd) == 0 && mrand.Float64() < 0.5))
	// 是为了减少自私挖矿的可能性。
	reorg := externTd.Cmp(localTd) > 0
	if !reorg && externTd.Cmp(localTd) == 0 {
		// Split same-difficulty blocks by number, then at random
		reorg = block.NumberU64() < bc.currentBlock.NumberU64() || (block.NumberU64() == bc.currentBlock.NumberU64() && mrand.Float64() < 0.5)
	}
	if reorg {
		// Reorganise the chain if the parent is not the head block
		// 如果这个区块的父区块不是当前的区块，说明存在一个分叉。需要调用 reorg 重新组织区块链。
		if block.ParentHash() != bc.currentBlock.Hash() {
			if err := bc.reorg(bc.currentBlock, block); err != nil {
				return NonStatTy, err
			}
		}
		// Write the positional metadata for transaction and receipt lookups
		// "l" + txHash -> {blockHash,blockNum,txIndex}
		// 根据交易的 hash 值来找到对应的区块以及对应的交易。
		if err := WriteTxLookupEntries(batch, block); err != nil {
			return NonStatTy, err
		}
		// Write hash preimages
		// hash(Keccak-256) -> 对应的数据 这个功能是用来测试的。如果开启了dev 模式，
		// 或者是 vmdebug 参数， 如果执行 SHA3 指令就会添加 Preimage
		if err := WritePreimages(bc.chainDb, block.NumberU64(), state.Preimages()); err != nil {
			return NonStatTy, err
		}
		status = CanonStatTy
	} else {
		status = SideStatTy
	}
	if err := batch.Write(); err != nil {
		return NonStatTy, err
	}

	// Set new head.
	if status == CanonStatTy {
		bc.insert(block)
	}
	bc.futureBlocks.Remove(block.Hash())
	return status, nil
}

// InsertChain attempts to insert the given batch of blocks in to the canonical
// chain or, otherwise, create a fork. If an error is returned it will return
// the index number of the failing block as well an error describing what went
// wrong.
//
// After insertion is done, all accumulated events will be fired.
// 在插入完成之后,所有累计的事件将被触发
func (bc *BlockChain) InsertChain(chain types.Blocks) (int, error) {
	n, events, logs, err := bc.insertChain(chain)
	bc.PostChainEvents(events, logs)
	return n, err
}

// insertChain will execute the actual chain insertion and event aggregation. The
// only reason this method exists as a separate one is to make locking cleaner
// with deferred statements.
func (bc *BlockChain) insertChain(chain types.Blocks) (int, []interface{}, []*types.Log, error) {
	// Do a sanity check that the provided chain is actually ordered and linked
	// 做一个健全的检查，提供的链实际上是有序的和相互链接的
	for i := 1; i < len(chain); i++ {
		if chain[i].NumberU64() != chain[i-1].NumberU64()+1 || chain[i].ParentHash() != chain[i-1].Hash() {
			// Chain broke ancestry, log a messge (programming error) and skip insertion
			log.Error("Non contiguous block insert", "number", chain[i].Number(), "hash", chain[i].Hash(),
				"parent", chain[i].ParentHash(), "prevnumber", chain[i-1].Number(), "prevhash", chain[i-1].Hash())

			return 0, nil, nil, fmt.Errorf("non contiguous insert: item %d is #%d [%x…], item %d is #%d [%x…] (parent [%x…])", i-1, chain[i-1].NumberU64(),
				chain[i-1].Hash().Bytes()[:4], i, chain[i].NumberU64(), chain[i].Hash().Bytes()[:4], chain[i].ParentHash().Bytes()[:4])
		}
	}
	// Pre-checks passed, start the full block imports
	bc.wg.Add(1)
	defer bc.wg.Done()

	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	// A queued approach to delivering events. This is generally
	// faster than direct delivery and requires much less mutex
	// acquiring.
	var (
		stats         = insertStats{startTime: mclock.Now()}
		events        = make([]interface{}, 0, len(chain))
		lastCanon     *types.Block
		coalescedLogs []*types.Log
	)
	// Start the parallel header verifier
	headers := make([]*types.Header, len(chain))
	seals := make([]bool, len(chain))

	for i, block := range chain {
		headers[i] = block.Header()
		seals[i] = true
	}
	// 调用共识擎来验证区块头是有效的
	abort, results := bc.engine.VerifyHeaders(bc, headers, seals)
	defer close(abort)

	// Iterate over the blocks and insert when the verifier permits
	for i, block := range chain {
		// If the chain is terminating, stop processing blocks
		if atomic.LoadInt32(&bc.procInterrupt) == 1 {
			log.Debug("Premature abort during blocks processing")
			break
		}
		// If the header is a banned one, straight out abort
		// 如果区块头被禁止了
		if BadHashes[block.Hash()] {
			bc.reportBlock(block, nil, ErrBlacklistedHash)
			return i, events, coalescedLogs, ErrBlacklistedHash
		}
		// Wait for the block's verification to complete
		bstart := time.Now()

		err := <-results
		// 如果没有错误，验证 body
		if err == nil {
			err = bc.Validator().ValidateBody(block)
		}
		// 如果区块已经插入, 直接继续
		if err != nil {
			if err == ErrKnownBlock {
				stats.ignored++
				continue
			}

			if err == consensus.ErrFutureBlock {
				// Allow up to MaxFuture second in the future blocks. If this limit
				// is exceeded the chain is discarded and processed at a later time
				// if given.
				// 如果是未来的区块，而且区块的时间距离现在不是很久远，那么存放起来。
				max := big.NewInt(time.Now().Unix() + maxTimeFutureBlocks)
				if block.Time().Cmp(max) > 0 {
					return i, events, coalescedLogs, fmt.Errorf("future block: %v > %v", block.Time(), max)
				}
				bc.futureBlocks.Add(block.Hash(), block)
				stats.queued++
				continue
			}
			// 如果区块没有找到祖先 而在 future blocks 包含了这个区块的祖先，那么也存放在 future
			if err == consensus.ErrUnknownAncestor && bc.futureBlocks.Contains(block.ParentHash()) {
				bc.futureBlocks.Add(block.Hash(), block)
				stats.queued++
				continue
			}

			bc.reportBlock(block, nil, err)
			return i, events, coalescedLogs, err
		}
		// Create a new statedb using the parent block and report an
		// error if it fails.
		var parent *types.Block
		if i == 0 {
			parent = bc.GetBlock(block.ParentHash(), block.NumberU64()-1)
		} else {
			parent = chain[i-1]
		}
		state, err := state.New(parent.Root(), bc.stateCache)
		if err != nil {
			return i, events, coalescedLogs, err
		}
		// Process block using the parent state as reference point.
		// 处理区块，生成交易，收据，日志等信息。
		// 实际上调用了 state_processor.go 里面的 Process 方法
		receipts, logs, usedGas, err := bc.processor.Process(block, state, bc.vmConfig)
		if err != nil {
			bc.reportBlock(block, receipts, err)
			return i, events, coalescedLogs, err
		}
		// Validate the state using the default validator
		// 二次验证，验证状态是否合法
		err = bc.Validator().ValidateState(block, parent, state, receipts, usedGas)
		if err != nil {
			bc.reportBlock(block, receipts, err)
			return i, events, coalescedLogs, err
		}
		// Write the block to the chain and get the status.
		// 写入区块和状态
		status, err := bc.WriteBlockAndState(block, receipts, state)
		if err != nil {
			return i, events, coalescedLogs, err
		}
		switch status {
		// 插入了新的区块
		case CanonStatTy:
			log.Debug("Inserted new block", "number", block.Number(), "hash", block.Hash(), "uncles", len(block.Uncles()),
				"txs", len(block.Transactions()), "gas", block.GasUsed(), "elapsed", common.PrettyDuration(time.Since(bstart)))

			coalescedLogs = append(coalescedLogs, logs...)
			blockInsertTimer.UpdateSince(bstart)
			events = append(events, ChainEvent{block, block.Hash(), logs})
			lastCanon = block

		// 插入了一个 forked 区块
		case SideStatTy:
			log.Debug("Inserted forked block", "number", block.Number(), "hash", block.Hash(), "diff", block.Difficulty(), "elapsed",
				common.PrettyDuration(time.Since(bstart)), "txs", len(block.Transactions()), "gas", block.GasUsed(), "uncles", len(block.Uncles()))

			blockInsertTimer.UpdateSince(bstart)
			events = append(events, ChainSideEvent{block})
		}
		stats.processed++
		stats.usedGas += usedGas.Uint64()
		stats.report(chain, i)
	}
	// Append a single chain head event if we've progressed the chain
	// 如果我们生成了一个新的区块头，而且最新的区块头等于 lastCanon
	// 那么我们公布一个新的 ChainHeadEvent
	if lastCanon != nil && bc.LastBlockHash() == lastCanon.Hash() {
		events = append(events, ChainHeadEvent{lastCanon})
	}
	return 0, events, coalescedLogs, nil
}

// insertStats tracks and reports on block insertion.
type insertStats struct {
	queued, processed, ignored int
	usedGas                    uint64
	lastIndex                  int
	startTime                  mclock.AbsTime
}

// statsReportLimit is the time limit during import after which we always print
// out progress. This avoids the user wondering what's going on.
const statsReportLimit = 8 * time.Second

// report prints statistics if some number of blocks have been processed
// or more than a few seconds have passed since the last message.
func (st *insertStats) report(chain []*types.Block, index int) {
	// Fetch the timings for the batch
	var (
		now     = mclock.Now()
		elapsed = time.Duration(now) - time.Duration(st.startTime)
	)
	// If we're at the last block of the batch or report period reached, log
	if index == len(chain)-1 || elapsed >= statsReportLimit {
		var (
			end = chain[index]
			txs = countTransactions(chain[st.lastIndex : index+1])
		)
		context := []interface{}{
			"blocks", st.processed, "txs", txs, "mgas", float64(st.usedGas) / 1000000,
			"elapsed", common.PrettyDuration(elapsed), "mgasps", float64(st.usedGas) * 1000 / float64(elapsed),
			"number", end.Number(), "hash", end.Hash(),
		}
		if st.queued > 0 {
			context = append(context, []interface{}{"queued", st.queued}...)
		}
		if st.ignored > 0 {
			context = append(context, []interface{}{"ignored", st.ignored}...)
		}
		log.Info("Imported new chain segment", context...)

		*st = insertStats{startTime: now, lastIndex: index + 1}
	}
}

func countTransactions(chain []*types.Block) (c int) {
	for _, b := range chain {
		c += len(b.Transactions())
	}
	return c
}

// reorgs takes two blocks, an old chain and a new chain and will reconstruct the blocks and inserts them
// to be part of the new canonical chain and accumulates potential missing transactions and post an
// event about them
// reorgs 接受两个区块作为参数，一个是老的区块链，一个新的区块链，这个方法会把他们插入
// 以便重新构建出一条规范的区块链。 同时会累计潜在会丢失的交易并把它们作为事件发布出去。
func (bc *BlockChain) reorg(oldBlock, newBlock *types.Block) error {
	var (
		newChain    types.Blocks
		oldChain    types.Blocks
		commonBlock *types.Block
		deletedTxs  types.Transactions
		deletedLogs []*types.Log
		// collectLogs collects the logs that were generated during the
		// processing of the block that corresponds with the given hash.
		// These logs are later announced as deleted.
		// collectLogs 会收集我们已经生成的日志信息，
		// 这些日志稍后会被声明删除(实际上在数据库中并没有被删除)。
		collectLogs = func(h common.Hash) {
			// Coalesce logs and set 'Removed'.
			receipts := GetBlockReceipts(bc.chainDb, h, bc.hc.GetBlockNumber(h))
			for _, receipt := range receipts {
				for _, log := range receipt.Logs {
					del := *log
					del.Removed = true
					deletedLogs = append(deletedLogs, &del)
				}
			}
		}
	)

	// first reduce whoever is higher bound
	if oldBlock.NumberU64() > newBlock.NumberU64() {
		// reduce old chain
		// 如果老的链比新的链高。那么需要减少老的链，让它和新链一样高
		for ; oldBlock != nil && oldBlock.NumberU64() != newBlock.NumberU64(); oldBlock = bc.GetBlock(oldBlock.ParentHash(), oldBlock.NumberU64()-1) {
			oldChain = append(oldChain, oldBlock)
			deletedTxs = append(deletedTxs, oldBlock.Transactions()...)

			collectLogs(oldBlock.Hash())
		}
	} else {
		// reduce new chain and append new chain blocks for inserting later on
		// 如果新链比老链要高，那么减少新链。
		for ; newBlock != nil && newBlock.NumberU64() != oldBlock.NumberU64(); newBlock = bc.GetBlock(newBlock.ParentHash(), newBlock.NumberU64()-1) {
			newChain = append(newChain, newBlock)
		}
	}
	if oldBlock == nil {
		return fmt.Errorf("Invalid old chain")
	}
	if newBlock == nil {
		return fmt.Errorf("Invalid new chain")
	}

	// 这个 for 循环里面需要找到共同的祖先。
	for {
		if oldBlock.Hash() == newBlock.Hash() {
			commonBlock = oldBlock
			break
		}

		oldChain = append(oldChain, oldBlock)
		newChain = append(newChain, newBlock)
		deletedTxs = append(deletedTxs, oldBlock.Transactions()...)
		collectLogs(oldBlock.Hash())

		oldBlock, newBlock = bc.GetBlock(oldBlock.ParentHash(), oldBlock.NumberU64()-1), bc.GetBlock(newBlock.ParentHash(), newBlock.NumberU64()-1)
		if oldBlock == nil {
			return fmt.Errorf("Invalid old chain")
		}
		if newBlock == nil {
			return fmt.Errorf("Invalid new chain")
		}
	}
	// Ensure the user sees large reorgs
	if len(oldChain) > 0 && len(newChain) > 0 {
		logFn := log.Debug
		if len(oldChain) > 63 {
			logFn = log.Warn
		}
		logFn("Chain split detected", "number", commonBlock.Number(), "hash", commonBlock.Hash(),
			"drop", len(oldChain), "dropfrom", oldChain[0].Hash(), "add", len(newChain), "addfrom", newChain[0].Hash())
	} else {
		log.Error("Impossible reorg, please file an issue", "oldnum", oldBlock.Number(), "oldhash", oldBlock.Hash(), "newnum", newBlock.Number(), "newhash", newBlock.Hash())
	}
	var addedTxs types.Transactions
	// insert blocks. Order does not matter. Last block will be written in ImportChain itself which creates the new head properly
	for _, block := range newChain {
		// insert the block in the canonical way, re-writing history
		// 插入区块 更新记录规范区块链的 key
		bc.insert(block)
		// write lookup entries for hash based transaction/receipt searches
		// 写入交易的查询信息
		if err := WriteTxLookupEntries(bc.chainDb, block); err != nil {
			return err
		}
		addedTxs = append(addedTxs, block.Transactions()...)
	}

	// calculate the difference between deleted and added transactions
	diff := types.TxDifference(deletedTxs, addedTxs)
	// When transactions get deleted from the database that means the
	// receipts that were created in the fork must also be deleted
	// 删除那些需要删除的交易查询信息。
	// 这里并没有删除那些需要删除的区块，区块头，收据等信息。
	for _, tx := range diff {
		DeleteTxLookupEntry(bc.chainDb, tx.Hash())
	}
	// 发送消息通知
	if len(deletedLogs) > 0 {
		go bc.rmLogsFeed.Send(RemovedLogsEvent{deletedLogs})
	}
	if len(oldChain) > 0 {
		go func() {
			for _, block := range oldChain {  // 发送消息通知
				bc.chainSideFeed.Send(ChainSideEvent{Block: block})
			}
		}()
	}

	return nil
}

// PostChainEvents iterates over the events generated by a chain insertion and
// posts them into the event feed.
// TODO: Should not expose PostChainEvents. The chain events should be posted in WriteBlock.
func (bc *BlockChain) PostChainEvents(events []interface{}, logs []*types.Log) {
	// post event logs for further processing
	if logs != nil {
		bc.logsFeed.Send(logs)
	}
	for _, event := range events {
		switch ev := event.(type) {
		case ChainEvent:
			bc.chainFeed.Send(ev)

		case ChainHeadEvent:
			bc.chainHeadFeed.Send(ev)

		case ChainSideEvent:
			bc.chainSideFeed.Send(ev)
		}
	}
}

func (bc *BlockChain) update() {
	futureTimer := time.Tick(5 * time.Second)
	for {
		select {
		case <-futureTimer:
			bc.procFutureBlocks()
		case <-bc.quit:
			return
		}
	}
}

// BadBlockArgs represents the entries in the list returned when bad blocks are queried.
type BadBlockArgs struct {
	Hash   common.Hash   `json:"hash"`
	Header *types.Header `json:"header"`
}

// BadBlocks returns a list of the last 'bad blocks' that the client has seen on the network
func (bc *BlockChain) BadBlocks() ([]BadBlockArgs, error) {
	headers := make([]BadBlockArgs, 0, bc.badBlocks.Len())
	for _, hash := range bc.badBlocks.Keys() {
		if hdr, exist := bc.badBlocks.Peek(hash); exist {
			header := hdr.(*types.Header)
			headers = append(headers, BadBlockArgs{header.Hash(), header})
		}
	}
	return headers, nil
}

// addBadBlock adds a bad block to the bad-block LRU cache
func (bc *BlockChain) addBadBlock(block *types.Block) {
	bc.badBlocks.Add(block.Header().Hash(), block.Header())
}

// reportBlock logs a bad block error.
func (bc *BlockChain) reportBlock(block *types.Block, receipts types.Receipts, err error) {
	bc.addBadBlock(block)

	var receiptString string
	for _, receipt := range receipts {
		receiptString += fmt.Sprintf("\t%v\n", receipt)
	}
	log.Error(fmt.Sprintf(`
########## BAD BLOCK #########
Chain config: %v

Number: %v
Hash: 0x%x
%v

Error: %v
##############################
`, bc.config, block.Number(), block.Hash(), receiptString, err))
}

// InsertHeaderChain attempts to insert the given header chain in to the local
// chain, possibly creating a reorg. If an error is returned, it will return the
// index number of the failing header as well an error describing what went wrong.
//
// The verify parameter can be used to fine tune whether nonce verification
// should be done or not. The reason behind the optional check is because some
// of the header retrieval mechanisms already need to verify nonces, as well as
// because nonces can be verified sparsely, not needing to check each.
func (bc *BlockChain) InsertHeaderChain(chain []*types.Header, checkFreq int) (int, error) {
	start := time.Now()
	if i, err := bc.hc.ValidateHeaderChain(chain, checkFreq); err != nil {
		return i, err
	}

	// Make sure only one thread manipulates the chain at once
	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	bc.wg.Add(1)
	defer bc.wg.Done()

	whFunc := func(header *types.Header) error {
		bc.mu.Lock()
		defer bc.mu.Unlock()

		_, err := bc.hc.WriteHeader(header)
		return err
	}

	return bc.hc.InsertHeaderChain(chain, whFunc, start)
}

// writeHeader writes a header into the local chain, given that its parent is
// already known. If the total difficulty of the newly inserted header becomes
// greater than the current known TD, the canonical chain is re-routed.
//
// Note: This method is not concurrent-safe with inserting blocks simultaneously
// into the chain, as side effects caused by reorganisations cannot be emulated
// without the real blocks. Hence, writing headers directly should only be done
// in two scenarios: pure-header mode of operation (light clients), or properly
// separated header/block phases (non-archive clients).
func (bc *BlockChain) writeHeader(header *types.Header) error {
	bc.wg.Add(1)
	defer bc.wg.Done()

	bc.mu.Lock()
	defer bc.mu.Unlock()

	_, err := bc.hc.WriteHeader(header)
	return err
}

// CurrentHeader retrieves the current head header of the canonical chain. The
// header is retrieved from the HeaderChain's internal cache.
func (bc *BlockChain) CurrentHeader() *types.Header {
	bc.mu.RLock()
	defer bc.mu.RUnlock()

	return bc.hc.CurrentHeader()
}

// GetTd retrieves a block's total difficulty in the canonical chain from the
// database by hash and number, caching it if found.
func (bc *BlockChain) GetTd(hash common.Hash, number uint64) *big.Int {
	return bc.hc.GetTd(hash, number)
}

// GetTdByHash retrieves a block's total difficulty in the canonical chain from the
// database by hash, caching it if found.
func (bc *BlockChain) GetTdByHash(hash common.Hash) *big.Int {
	return bc.hc.GetTdByHash(hash)
}

// GetHeader retrieves a block header from the database by hash and number,
// caching it if found.
func (bc *BlockChain) GetHeader(hash common.Hash, number uint64) *types.Header {
	return bc.hc.GetHeader(hash, number)
}

// GetHeaderByHash retrieves a block header from the database by hash, caching it if
// found.
func (bc *BlockChain) GetHeaderByHash(hash common.Hash) *types.Header {
	return bc.hc.GetHeaderByHash(hash)
}

// HasHeader checks if a block header is present in the database or not, caching
// it if present.
func (bc *BlockChain) HasHeader(hash common.Hash, number uint64) bool {
	return bc.hc.HasHeader(hash, number)
}

// GetBlockHashesFromHash retrieves a number of block hashes starting at a given
// hash, fetching towards the genesis block.
func (bc *BlockChain) GetBlockHashesFromHash(hash common.Hash, max uint64) []common.Hash {
	return bc.hc.GetBlockHashesFromHash(hash, max)
}

// GetHeaderByNumber retrieves a block header from the database by number,
// caching it (associated with its hash) if found.
func (bc *BlockChain) GetHeaderByNumber(number uint64) *types.Header {
	return bc.hc.GetHeaderByNumber(number)
}

// Config retrieves the blockchain's chain configuration.
func (bc *BlockChain) Config() *params.ChainConfig { return bc.config }

// Engine retrieves the blockchain's consensus engine.
func (bc *BlockChain) Engine() consensus.Engine { return bc.engine }

// SubscribeRemovedLogsEvent registers a subscription of RemovedLogsEvent.
func (bc *BlockChain) SubscribeRemovedLogsEvent(ch chan<- RemovedLogsEvent) event.Subscription {
	return bc.scope.Track(bc.rmLogsFeed.Subscribe(ch))
}

// SubscribeChainEvent registers a subscription of ChainEvent.
func (bc *BlockChain) SubscribeChainEvent(ch chan<- ChainEvent) event.Subscription {
	return bc.scope.Track(bc.chainFeed.Subscribe(ch))
}

// SubscribeChainHeadEvent registers a subscription of ChainHeadEvent.
func (bc *BlockChain) SubscribeChainHeadEvent(ch chan<- ChainHeadEvent) event.Subscription {
	return bc.scope.Track(bc.chainHeadFeed.Subscribe(ch))
}

// SubscribeChainSideEvent registers a subscription of ChainSideEvent.
func (bc *BlockChain) SubscribeChainSideEvent(ch chan<- ChainSideEvent) event.Subscription {
	return bc.scope.Track(bc.chainSideFeed.Subscribe(ch))
}

// SubscribeLogsEvent registers a subscription of []*types.Log.
func (bc *BlockChain) SubscribeLogsEvent(ch chan<- []*types.Log) event.Subscription {
	return bc.scope.Track(bc.logsFeed.Subscribe(ch))
}
